1. Field of the Invention
The invention relates to a process and apparatus for interrogating a storage phosphor screen, and more particularly to an improved process and apparatus for retrieving information of improved resolution and sensitivity from a storage phosphor screen.
2. Description of the Prior Art
Ionizing radiation images have been and continue to be used as basic investigative tools in medicine, industry and science. There are two general categories of phosphor-based imaging systems. The first employs phosphors chosen from the scintillators wherein the incident ionizing radiation interacts with the phosphor to immediately produce a visible-light image. The second employs photostimulable storage phosphors wherein the phosphor temporarily stores the incident radiation patterns for retrieval as infrared or visible-light images an interval of time later by scanning or flooding with electromagnetic radiation, such as described in: U.S. Pat. No. 3,859,527 to Luckey, or U.S. Pat. No. 4,239,968 to Kotera, et al., or U.S. Pat. No. 5,065,023 to Lindmayer, or U.S. Pat. No. 4,733,090 to DeBoer, et al.
In both types of system, there is an inverse relationship between two fundamental determinants of image quality, namely: resolution, referring to the sharpness or the spatial detail evident in an image; and sensitivity, referring to the energy conversion efficiency from the ionizing radiation to the luminescent image. Generally, sensitivity is increased by using a thicker phosphor layer thereby increasing the probability of interaction between the radiation and the phosphor layer, but the resulting luminescence is more widely scattered thereby decreasing resolution. Conversely, increasing resolution by decreasing phosphor thickness decreases the probability of interaction, and therefore, sensitivity.
Several methods to improve this reverse relationship have been disclosed, such as, for example in U.S. Pat. No. 4,637,898 to DeBoer et al.; U.S. Pat. No. 4,906,850 to Beerlage; U.S. Pat. No. 5,410,144 to Mouyen; U.S. Pat. No. 5,065,023 to Lindmayer; and U.S. Pat. No. 5,124,588 to Soltani et al.
There remains the continuing need for improved process and apparatus to retrieve information of improved spatial resolution and sensitivity with lower exposure from a storage phosphor screen.